Channel scanning is a generally known technique used by mobile stations to find the communications channels that can be used to connect with a base station and therefore with a communications network. When a mobile station, such as a mobile phone, is powered on, it shall search an available channel for connection with the network. The same happens when the mobile phone loses connection to the network; it must find a usable channel as soon as possible to become connected again.
Generally, wireless communications systems have well-defined frequency bands and channel plans, which are also harmonized over many countries before a wireless communications standard is widely deployed. Moreover, a typical mobile station is pre-provisioned for a given operator, and is configured with the list of channels used by this operator as well as the channels plans for the main roaming partners of that operator. In this context, a mobile station trying to enter the network will typically use a gradual approach, for example, the mobile will first try the channel of its last serving base station, and if that fails, it will try to connect to the network by using any one channel of a set of channels whose configuration (frequency and bandwidth) has been previously defined and stored in the mobile station. If the mobile station cannot connect to the network using a certain channel configuration of the set, it will try with another channel configuration of that set, and so on, in a trial and error search approach until it finds the channel configuration available in that location for connection to the network.
However, the channel search can require a significant amount of time, particularly if the number of channels of the set to be searched is large. This delays the network connection time and degrades the communications service experience. Indeed, users will find objectionable to wait a long time after turning on a mobile station before obtaining a channel and being able to start communication.
Therefore, there is a need to find a solution to the above problem, and reduce the time a mobile station needs to find a suitable channel to connect to the network. A known solution, for example, is disclosed in U.S. Pat. No. 6,434,186, where the mobile station is provided with a certain channel plan or Preferred Roaming List, i.e. a set of predetermined channels (defined by their center frequency and bandwidth) the mobile station may use to connect with the network, but, instead of trying to connect to the network using each channel of the set, the mobile station first performs a spectral analysis of each channel of the set in order to recognize whether each channel contains a signal of a certain wireless communication technology (e.g. A CDMA signal) or not. Then that information is used to determine which channels of the set are more likely to be CDMA channels, and to search these channels first (i.e., with a higher priority), or to only search these channels. The number of attempts for connection to the network is thereby reduced and consequently also the connection time.
Another known solution is disclosed in U.S. Pat. No. 6,434,186, in which the mobile station is provided with a certain channel plan, but, instead of trying to connect to the network using each channel of the set, the mobile station first uses a wide bandwidth reception mode in order to detect wide bandwidth segments which contain a significant signal energy (e.g. said segments are prioritized according to the signal strength detected) and then using a narrowband reception mode to detect the channels of each wide bandwidth that contain the strongest signal. According to this approach, each channel of the set is prioritized by signal strength and attempts to connect with the network are first done with those channels with higher priority (the ones containing the strongest signal).
Nevertheless, while the above solutions reduce the network connection time by prioritizing the channels for which a connection attempt shall be done, they still rely on a certain pre-provisioned channel list stored in the mobile station. This may be suitable for 2G and certain 3G wireless communications standards for which the pre-provisional channel list can be maintained within a certain complexity limit, but will not be suitable for certain standards, e.g. WiMAX or 3GPP LTE, in which the number of possible channel configurations to test increases significantly. For WIMAX, for example, the diversity of channel configurations may substantially vary from operator to operator and from country to country, and many configurations can be used by the operators concerning channel bandwidth (e.g. 3, 3.5, 5, 7, 8.75 and/or 10 MHz) and the frequency bands to be used by the wireless communication devices (e.g. 700 MHz, 1.6 GHz, 2.3 GHz, 2.5 GHz and/or 3.5 GHz). For each frequency band a trial and error approach would need several connection attempts and the wireless communications equipment may, for example, need to search channels in at least a 600 MHz bandwidth. Additionally, many wireless communication devices may be sold without being pre-provisioned with a list of possible channels which can be used to connect with the network.
Still another known solution, which is considered the closes state of the art, is disclosed in U.S. Pat. No. 6,714,605, in which a real-time spectrum analysis engine (SAGE) is provided to generate information about the signal activity in a frequency band. The SAGE comprises a spectrum analyzer component, which generates data representing a real-time spectrogram of a bandwidth radio frequency spectrum, and a signal detector component, which detects signal pulses in a frequency band and outputs pulse event information. The signal detector comprises a peak detector, which detects one or more peaks in a spectral information of a frequency band and a pulse detector, which, for each detected peak, determines whether it is a signal pulse that satisfies one or more characteristics.
However, the peak detection techniques used in the above-cited document are not able to perfectly identify and characterize all the communications channels of a frequency band since they do not take in consideration the different frequency representation of channels from different communications standards. Indeed, signal detection and characterization is done, on the other hand, based on pre-provisioned pulse detection rules which depend on the frequency band analyzed. The solution, therefore does not adapt to certain communications standards in which the diversity of channel configurations may substantially vary from operator to operator and from country to country, since the pre-provisioned pulse detection rules to be applied and tested would increase the complexity of identifying the channel characteristics. The solution does not adapt either for channel scanning in frequency bands with at least 600 MHz of bandwidth.